This invention relates generally to a control circuit for a gas furnace which automatically resets itself when it is in a lockout condition by timing the length of time that the thermostat has been "closed" and calling for heat.
U.S. Pat. No. 4,325,689 to Burke discloses a furnace reset which directly senses that the flame is extinguished and a timer is employed to delay the "re-light" attempt until a predetermined time interval after the flame has gone out to prevent a hazardous condition.
U.S. Pat. No. 4,773,586 to Ryan shows a safety sense element 28 which energizes the blower relay of the furnace when a high furnace temperature causes limit thermostat 18 to "open". But, no means is provided for automatic reset of the furnace after a lockout has occurred.
The principal object of this invention is to automatically reset an unattended gas furnace when the primary control of the furnace has gone into a lockout condition for a predetermined time duration.
Another object of this invention is to provide an electrical circuit for a furnace which automatically monitors the furnace control and simulates the effect of manually resetting or lowering the thermostat to reset the furnace control from a lockout condition.
Still another object of this invention is to ensure that unattended furnaces which have gone into a lockout condition will not be left in that condition for an extended period of time with the potential in winter of the water freezing and bursting the pipes with potential of damage to the unattended space and its contents.
A further object of this invention is to provide means for resetting a furnace from a locked out state which does not depend upon the direct sensing of the burner flame, but rather simulates the effect of resetting the thermostat.